netdev - Re: [PATCH net-next v6 1/3] rculist: Add hlist_nulls_replace_rcu() and hlist_nulls_replace_init

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Message-ID: <15ce9ffb-fdd0-4dba-8cfa-b24de99368fb@linux.dev>
Date: Fri, 26 Sep 2025 12:33:19 +0800
From: luoxuanqiang <xuanqiang.luo@...ux.dev>
To: Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: edumazet@...gle.com, "Paul E. McKenney" <paulmck@...nel.org>,
 kerneljasonxing@...il.com, davem@...emloft.net, kuba@...nel.org,
 netdev@...r.kernel.org, Xuanqiang Luo <luoxuanqiang@...inos.cn>,
 Frederic Weisbecker <frederic@...nel.org>,
 Neeraj Upadhyay <neeraj.upadhyay@...nel.org>
Subject: Re: [PATCH net-next v6 1/3] rculist: Add hlist_nulls_replace_rcu()
 and hlist_nulls_replace_init_rcu()

在 2025/9/26 12:02, Kuniyuki Iwashima 写道:
> On Thu, Sep 25, 2025 at 8:23 PM luoxuanqiang <xuanqiang.luo@...ux.dev> wrote:
> [...]
>>>> +{
>>>> +       struct hlist_nulls_node *next = old->next;
>>>> +
>>>> +       WRITE_ONCE(new->next, next);
>>>> +       WRITE_ONCE(new->pprev, old->pprev);
>>>> +       rcu_assign_pointer(*(struct hlist_nulls_node __rcu **)new->pprev, new);
>>> nit: define hlist_nulls_prev_rcu() like hlist_nulls_next_rcu().
>> I'm wondering if defining a macro called hlist_nulls_prev_rcu() might
>> be controversial, since it should actually be getting the prev->next
>> rather than the prev itself.
> See hlist_add_before_rcu() for an example:
>
>      rcu_assign_pointer(hlist_pprev_rcu(n), n);
>
> You can define hlist_nulls_pprev_rcu() and use it alike.
>
>      rcu_assign_pointer(hlist_nulls_pprev_rcu(new), new);
>
>
> [...]
>> However, I noticed that in the definition of hlist_pprev_rcu(), it directly
>> uses pprev:
>>
>> #define hlist_pprev_rcu(node)    (*((struct hlist_node __rcu **)((node)->pprev)))
> Note it dereferences *((node)->pprev).  The macro is not to iterate the
> lengthy cast.

Thank you for the quick and clear explanation!

I'll apply these changes in the next version.

Appreciate it!